The present invention relates in general to an exhaust gas purifying system of an internal combustion engine and more particularly to the system which retains the exhaust gases emitted from the engine for a prolonged period of time in an afterburning device so as to achieve complete combustion of harmful combustible compounds such as hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gases during deceleration and/or idling operation of the engine.
Some modernized internal combustion engine vehicles are equipped with afterburning devices such as oxidizing catalytic converters and/or thermal reactors in the exhaust systems thereof in order to completely burn out the remaining harmful combustible compounds such as hydrocarbons and carbon monoxide in the exhaust gases exhausted from the engine before the exhaust gases are discharged into the open air.
Apart from this, it is recognized that the rapid deceleration and/or idling operation of a carburetor type internal combustion engine causes the engine to produce increased amounts of the harmful combustible compounds. This is because, under such conditions the throttle valve of the carburetor is almost closed thus reducing the air induction into the combustion chambers of the engine. Thus, the air-fuel mixture in the combustion chambers becomes extremely rich with incomplete burning resulting.
Usually, the amount of the harmful compounds emitted from the engine in the above-mentioned states is excessive and cannot be completely treated or burnt sufficently rapidly by the afterburning device in the exhaust system of the engine, thus some of the remaining harmful compounds are discharged into the atmosphere.